The invention relates to an intraocular lens having a central lens area and a surrounding annular lens area.
1. Prior Art
An intraocular lens of this type is known from EP 0 537 643 B1. This lens may be designed as a monofocal lens, and consequently be made relatively thin, by the optical power being made up of a refractive component and a diffractive component. The cut to be made to the eye during the implantation can be kept small. Scatterings of light resulting from the diffractive fine structure component may influence the quality of the image produced on the retina.
2. Object of the invention
The object of the invention is to provide an intraocular lens of the type stated at the beginning in which an image with improved quality is produced on the retina with a low lens thickness.
This object is achieved according to the invention by an intraocular lens with an optical lens part, which has a central lens area and at least one further annular lens area surrounding said central lens area, the central lens area and the at least one annular lens area forming at least one common focus and the annular lens area having concentric annular zones, in which the difference in pathlength between adjacent zones is an integral multiple of n=2 or more of the design wavelength.
In the case of the intraocular lens according to the invention, arranged around a central lens area, which has refractive properties in particular, is at least one annular lens area, which forms a common focus with the central lens area, concentric annular zones arranged around the optical lens axis being provided in the annular lens area, the difference in the path length or difference in optical path between adjacent zones being an integral multiple of the design wavelength.
In a preferred way, the design wavelength is provided in the green spectral range of visible light, in the range of 550 nm for example.
The difference in path length of the adjacent zones may be set by the refractive index or by appropriate material selection and/or the geometry of the respective zone.
In a preferred way, the curvature of the meridial section of the optical lens part is aspherically formed, the zones with the differences in path length (differences in optical path) being provided in the edge region, in which the deviation of the aspherical profile from the spherical curve has an effect.
These annular zones, which are arranged concentrically around the optical lens axis, are formed in particular in a sawtooth shape. For forming a monofocal intraocular lens, these zones have the same optical power as the central, in particular refractive, lens area. Both parts contribute to a sharp image, which is produced on the retina of the eye.
For forming a bifocal lens, the optical lens part may be provided with an additional diffractive fine structure, which may extend over the entire optical lens part or, in a preferred way, is provided only on the central lens area, forming the refractive component. This is generally sufficient, since the bifocal function is required only when there is brightness corresponding to daylight and the pupillary aperture of the eye is essentially open only in the region of the central lens area, containing the refractive component. The additional diffractive fine structure, in particular in the form of concentric zones arranged around the optical lens axis, may be formed in such a way that adjacent zones produce a difference in path length of the optical path which is a fraction of the design wavelength, for example 0.4 or 0.6.
The invention is explained in more detail on the basis of exemplary embodiments with reference to the figures, in which: